Recently, the hard disk drive, representative of a magnetic disk device, is in a conspicuous trend toward the increase of recording density in order to realize small size and large capacity, whose track width is reduced down to 1 μm or smaller. In order for the head to correctly scan over such a narrow track, the head-tracking servo technology plays an important role. The presently available hard disk drive, using such track servo art, is to record a tracking servo signal, an address information signal, a reproducing clock signal, etc. at a constant angular interval in one turn of the disk. The drive device is to detect and rectify the head position according to those signals reproduced at a constant time interval from the head, thus allowing the head to correctly scan over the track.
Because the servo signal, the address information signal, the reproducing clock signal, etc. serve as reference signals for the head to correctly scan over the track, high positioning accuracy is required in the writing thereof (hereinafter, described “formatting”). In the presently available hard disk drive, formatting is performed by positioning in position the recording head with use of an exclusive servo device built with an accurate position detector utilizing light interference (hereinafter, referred to as a servo writer).
However, the following disadvantages exist in the formatting by means of the foregoing servo writer. Firstly, much time is required in writing signals over a multiplicity of tracks while accurately positioning the head in position. Thus, there is a need to operate many servo writers simultaneously in order to improve productivity. Secondly, a great deal of cost is needed in introducing many servo writers and maintaining/managing those. Such disadvantages are more serious as track density improves and track count increases.
In this situation, there is proposed a scheme and magnetic transfer apparatus that, by superimposing a disk called a master previously written with all pieces of servo information with a magnetic disk requiring formatting and then externally providing transfer energy to those, the information on the master is transferred in batch to the magnetic disk without using a servo writer in formatting (e.g. Japanese Patent Unexamined Publication No. H10-40544).
In the proposal, the substrate has a surface on which a magnetic region of ferromagnetic material is formed in a patterned form for information signals, thus being made as a magnetic transfer master. The magnetic transfer master at its surface is placed in contact with a surface of a sheet-formed or disk-like magnetic recording medium formed with a ferromagnetic thin film or ferromagnetic powder-applied layer, to which predetermined magnetic field is applied. Due to this, the method allows the magnetic recording medium to record a magnetized pattern having a patterned form corresponding to the information signal formed on the magnetic transfer master.
In the magnetic transfer device for use in the formatting according to the foregoing magnetic transfer scheme, formatting is available instantaneously. Nevertheless, in order to obtain preferable magnetic transfer signal quality, there is a need to place the magnetic transfer master and the magnetic disk in close contact with each other without any gap at the entire surfaces. For this purpose, it is significantly important to control the foreign matters and projections existing on a magnetic transfer master surface or a magnetic disk surface. Particularly, for the magnetic disk for magnetic transfer, it is vital to conduct a foreign-matter inspection without fail on the magnetic disk entirely in the planar surface thereof immediately before executing magnetic transfer.
As a foreign-matter inspection apparatus for use in a foreign-matter inspection on a planar region of a magnetic disk, there is known a foreign-matter inspection apparatus that scans a laser spot over a magnetic disk surface and inspects a foreign matter or projection on the magnetic disk by detecting the reflection light thereof (e.g. Japanese Patent Unexamined Publication No. 2003-4428).
FIG. 14 shows a foreign-matter inspection apparatus in the prior art. At the first step, by rotating inspection index 101 120 degrees, magnetic disk 102 to be inspected is transported to an inspection position where magnetic disk 102 lying in an inspection position is vacuum-held by inspection stage 103.
At the second step, the AD conversion board in computer 109 is notified of a sampling start.
At the third step, magnetic disk 102 is rotated by rotation driver 104 through inspection stage 103.
At the fourth step, a predetermined voltage is applied to laser light source 105, to emit laser light L1 to magnetic disk 102 on the inspection stage 103. The reflection light and scattering light of the same is received by light-reception camera 106 so that the image outputted from light-reception camera 106 is fetched to the A/D converter board of within computer 109. From the captured image, a foreign matter is detected by image recognition. This operation is performed several times by changing the laser-light irradiation position radially of the disk.
At the fifth step, laser light L2 is irradiated from dimension-measurer's illuminator 107 and passed through the lateral of an edge of magnetic disk 102. Otherwise, the laser light L2 scattered by the edge is received by dimension-measurer's light receiver 108 so that the A/D converter board in computer 109 can input therein a voltage value dependent upon the light-reception amount corresponding to the edge position.
At the sixth step, after terminating the sampling of voltage values (i.e. edge position measurement) during 360 degree rotation of magnetic disk 102, the voltage-value sampling result inputted to the A/D converter board is taken out to calculate a deviation amount (X, Y) from the setting value (0.0) of a rotating center of magnetic disk 102. At the sixth sequence, after detecting foreign matters on magnetic disk 102 throughout the entire area up to the outermost or the innermost, the deviation amount (X, Y) obtained at the fifth sequence is added to each of the obtained foreign-matter detection data.
Then, checking is made as to whether or not each foreign matter the deviation amount has been added has a coordinate lying inside or outside the inspection area. The detection data of a foreign matter lying outside is considered corresponding to the edge of magnetic disk 102 and excluded from the foreign-matter detection data. In this manner, because inspection is conducted while correctly measuring the outer peripheral edge position of magnetic disk 102, it is possible to exclude a erroneous recognition due to an irregular reflection at the outer peripheral edge. By scanning the laser light L1 up to the outer peripheral edge, foreign-matter detection can be effected thoroughly up to the outer peripheral edge.
However, the conventional foreign-matter inspection method and apparatus is to correctly measure the outer peripheral edge position of the disk, thus being required to use an expensive measuring instrument, such as a laser dimension measuring instrument. This raises a disadvantage of increasing apparatus price. Furthermore, because the disk is usually chamfered at its edge, the planar region to be inspected exists inward by a chamfer dimension from the outer peripheral edge. Generally, chamfer is low in working accuracy wherein chamfer dimension has a larger tolerance. Accordingly, even if the disk outer peripheral edge position is measured correctly, it is not easy to correctly determine a contour of the planar region to be inspected. Due to this, there is disadvantageously an increasing possibility to erroneously recognize the light irregularly reflected by the chamfer of the disk as light reflected from a foreign matter.